U.S. patent application number 10/499077 was filed with the patent office on 2005-01-27 for biaxially oriented polyester film.
Invention is credited to Kim, Sangil, Lee, Changju.
Application Number | 20050019595 10/499077 |
Document ID | / |
Family ID | 19716870 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050019595 |
Kind Code |
A1 |
Kim, Sangil ; et
al. |
January 27, 2005 |
Biaxially oriented polyester film
Abstract
The biaxially oriented polyester film of the present invention
useful for twist wrapping is prepared by biaxially drawing a
polyester sheet which has a glass transition temperature (Tg) of at
least 60.degree. C., in the longitudinal and transverse directions,
wherein the biaxially oriented film has a specific gravity of 1.38
or less.
Inventors: |
Kim, Sangil; (Kyungki-do,
KR) ; Lee, Changju; (Kyungki-do, KR) |
Correspondence
Address: |
ANDERSON, KILL & OLICK, P.C.
1251 AVENUE OF THE AMERICAS
NEW YORK,
NY
10020-1182
US
|
Family ID: |
19716870 |
Appl. No.: |
10/499077 |
Filed: |
June 10, 2004 |
PCT Filed: |
December 11, 2002 |
PCT NO: |
PCT/KR02/02336 |
Current U.S.
Class: |
428/480 ;
428/910; 528/272; 528/308; 528/308.6 |
Current CPC
Class: |
C08J 5/18 20130101; C08J
2367/02 20130101; Y10S 428/91 20130101; Y10T 428/31786
20150401 |
Class at
Publication: |
428/480 ;
428/910; 528/272; 528/308; 528/308.6 |
International
Class: |
B32B 027/36; C08G
063/16; C08G 063/181; C08G 063/183 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 11, 2001 |
KR |
10-2001-0078045 |
Claims
What is claimed is:
1. A biaxially oriented polyester film prepared by biaxially
drawing a polyester sheet which has a glass transition temperature
(Tg) of 60.degree. C. or higher, in the longitudinal and transverse
directions, wherein the biaxially oriented film has a specific
gravity of 1.38 or less and a dead-fold retainability of at least
60% defined as below: Dead-fold
retainability(%)=(180-.theta.).times.100/180 wherein .theta. is an
angle formed when a polyester film sheet is folded under a pressure
of 30 psi for 3 seconds at room temperature and the folded sheet is
kept at a vertical position for 1 hr.
2. The biaxially oriented polyester film of claim 1, wherein the
polyester sheet is prepared from one or more resins obtained by
polycondensation of a dicarboxylic acid component and an alkylene
glycol component.
3. The biaxially oriented film of claim 2, wherein the dicarboxylic
acid component comprises dimethyl terephthalate or terephthalic
acid.
4. The biaxially oriented film of claim 3, wherein the dicarboxylic
acid component further comprises at least one aromatic dicarboxylic
acid selected from the group consisting of isophthalic acid,
naphthalene dicarboxylic acid, dimethyl isophthalate,
dimethyl-2,6-naphthalene dicarboxylate.
5. The biaxially oriented film of claim 2, wherein the alkylene
glycol component comprises ethylene glycol.
6. The biaxially oriented film of claim 5, wherein the alkylene
glycol component further comprises at least one alkylene glycol
selected from the group consisting of diethylene glycol,
trimethylene glycol, tetramethylene glycol, 1,4-cyclohexane
dimethanol and 2,2-dimethyl(-1,3-propane)diol.
7. The biaxially oriented film of claim 1, wherein the
crystallization degree of the film is less than 40%.
8. The biaxially oriented film of claim 1, wherein the product of
drawing ratios in the longitudinal and transverse directions is in
the range of 4 to 20.
9. The biaxially oriented film of claim 1, wherein the drawing in
the longitudinal direction is conducted at a temperature in the
range of Tg of the polyester sheet and Tg+30.degree. C.
10. The biaxially oriented film of claim 1, wherein the drawing in
the transverse direction is conducted at a temperature in the range
of Tg of the polyester sheet+10.degree. C. and Tg+40.degree. C.
11. The biaxially oriented film of claim 1, wherein the refractive
indexes of the film in the longitudinal and transverse directions
are each 1.6 or higher.
12. The biaxially oriented film of claim 1, wherein the film is
used for twist wrapping.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to a biaxially oriented
polyester film for twist wrapping.
BACKGROUND OF THE INVENTION
[0002] Twist wrapping has been extensively used for wrapping
candies by twisting one or both of film ends. Such twist wrapping
films are formed of a cellophane film and a uniaxially oriented
polyethylene or polyvinyl chloride film.
[0003] However, cellophane films are disfavored because the cost of
production is high due to the necessity to treat toxic pollutants
emitted during manufacturing thereof. Uniaxially oriented
polyethylene or polyvinyl chloride films, on the other hand, have
the problem of insufficient twist fixing property.
[0004] Therefore, there has been attempts to prepare polyester
films having good twist wrapping properties and mechanical and
chemical properties, without any environmental or food hygienic
problems.
[0005] For example, Japanese Laid-open Patent Publication No. Hei
2-127022 discloses that a polyester film for twist wrapping can be
prepared by melt extruding a polyester resin having an intrinsic
viscosity of 0.5.about.1 and a melt viscosity of more than 2,300
poise at 265.degree. C., drawing at a ratio of 2.about.150, and
quenching between a first quenching roll having a temperature of
40.degree. C..about.glass transition temperature (Tg) and a second
quenching roll having a temperature of Tg.about.Tg+15.degree.
C.
[0006] Further, Japanese Laid-open No. Sho 61-277422 discloses a
process for preparing a polyester film having a haze of more than
6% by melt extruding a polyester copolymer manufactured from
terephthalic acid and a mixture of 1,4-butanediol and polyethylene
glycol of MW 106.about.550 and quenching by contacting the film
with a cooling drum of 50.about.80.degree. C. for more than 8
sec.
[0007] However, above processes suffer from poor processibility and
the printability of the resulting film is not satisfactory.
Meanwhile, Japanese Laid-open Publication No. Sho 57-102317
discloses a tubular polyester film for twist wrapping prepared by
extruding a polyester resin having an intrinsic viscosity of more
than 0.8 to attain a sheet and biaxially drawing the sheet at a
ratio of 3.about.4. Japanese Laid-open Publication No. Sho 57-66933
discloses a process for preparing a tubular polyester film having a
thickness of 60 micron or less by extruding a polyester resin
having an intrinsic viscosity of more than 0.72 and melt viscosity
of more than 6000 poise at 265.degree. C. through an annular die;
blowing at a blow ratio more than 1; and cold drawing.
[0008] However, such tubular films also have the problems of poor
processibility and unsatisfactory printability.
[0009] Japanese Laid-open Publication No. Sho 51-19049 discloses a
biaxially oriented polyester film comprising 95.about.30% by weight
of a polyester having a melting point of above 180.degree. C. and;
5.about.70% by weight of a low molecular weight polyester having an
intrinsic viscosity of 0.35 or less. However, this film easily
tears during the film making process.
SUMMARY OF THE INVENTION
[0010] Accordingly, it is a primary object of the present invention
to provide a polyester film having improved twist wrapping
property, printability and processibility in addition to improved
mechanical and chemical properties, environmental acceptability and
food sanitary safety.
[0011] The above object of the invention can be accomplished by a
biaxially oriented polyester film prepared by biaxially drawing a
polyester sheet having a glass transition temperature of not less
than 60.degree. C., wherein the film has a specific gravity of at
least 1.38.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The above and other objects and features of the present
invention will become apparent from the following description of
the invention, when taken in conjunction with the accompanying
drawings, which respectively show:
[0013] FIGS. 1 to 3: a schematic diagram for measuring a
retainability of dead-fold of the polyester film in accordance with
one embodiment of the present invention;
[0014] FIG. 4: a schematic diagram for measuring twist fixation in
transverse direction of the polyester film in accordance with one
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The biaxially oriented polyester film according to the
present invention has a dead-fold retainability of not less than
60%, which is defined by the following equation:
Dead-fold retainability(%)=(180-.theta.).times.100/180
[0016] wherein .theta. is the fold angle observed when a polyester
film sheet is folded under a pressure of 30 psi for 3 seconds at
room temperature and the folded sheet is kept at a vertical
position for 1 hr (cf FIG. 3)
[0017] The biaxially oriented polyester film according to the
present invention may be prepared by drawing a polyester sheet so
that the product of the longitudinal and transverse draw ratios is
in the range of 4 to 20.
[0018] According to the preferred example of the present invention,
drawing in the longitudinal direction is conducted at a temperature
between Tg of the polyester sheet and Tg+30.degree. C., and drawing
in the transverse direction, at Tg+10.degree.
C..about.Tg+40.degree. C.
[0019] The biaxially oriented polyester film according to the
present invention may have a refractive index of more than 1.6,
either the longitudinal or transverse direction.
[0020] The biaxially oriented polyester film according to the
present invention may be prepared by biaxially drawing a polyester
sheet in the longitudinal and transverse directions, the polyester
sheet being manufactured from one or more resins obtained by
polycondensating an acid component comprising an aromatic
dicarboxylic acid with a glycol component.
[0021] In a preferred embodiment, the aromatic dicarboxylic acid is
dimethyl terephthalate or terephthalic acid. It is also preferable
that the acid component further comprises other aromatic
dicarboxylic acid such as isophthalic acid, naphthalene
dicarboxylic acid, dimethyl isophthalate, dimethyl-2,6-naphthalene
dicarboxylate, etc.
[0022] It is preferable that the alkylene glycol is ethylene
glycol. It is also preferable that the alkylene glycol further
comprises other alkylene glycol component such as dimethylene
glycol, trimethylene glycol, teteramethylene glycol,
1,4-cyclohexane dimethanol or 2,2-dimethyl(-1,3-propane) diol.
[0023] In a preferred embodiment, Tg of the polyester resin used in
the present invention is 60.degree. C. or higher. If Tg of the
polyester resin is less than 60.degree. C., mechanical and thermal
properties of the polyester become unsatisfactory.
[0024] The polyester sheet used in the present invention may be
prepared from a blend of polyester resins obtained by polymerizing
the aforementioned aromatic dicarboxylic acid and glycol
component.
[0025] The biaxially oriented polyester film according to the
present invention may further comprise other components such as a
polycondensation catalyst, dispersant, electrostatic generator,
antistatic agent, antiblocking agent and inorganic lubricant.
[0026] The biaxially oriented polyester film according to the
present invention is prepared by biaxially drawing a polyester
sheet having a glass transition temperature of 60.degree. C. or
higher, wherein the film has a specific gravity of 1.38 or
less.
[0027] The specific gravity of a polyester film is a measure of
crystallinity of the film, and the relationship between a specific
gravity and crystallinity may be expressed as follows:
Xc={dc.times.(d-da)}.times.100/{d.times.(dc-da)}
[0028] wherein, Xc is crystallization degree (%), d is specific
gravity, dc is specific gravity at 100% crystallization (1.455 in
case of polyethylene terephthalate), and da is specific gravity at
100% amorphous (1.335 in case of polyethylene terephthalate).
[0029] According to the above equation, when the specific gravity
of a film is 1.38, the crystallization degree of the film is about
40%.
[0030] The crystallization degree of a polyester film is an
important factor influencing the retainability of dead-fold and
twist wrapping properties of film.
[0031] Thus, if the crystallization degree is more than 40%, the
dead-fold retainability and twist wrapping properties become
unsatisfactory.
[0032] The crystallization degree of a polyester film is generally
dependent on process conditions such as drawing ratio or drawing
temperature. The inventive polyester film is drawn in the
longitudinal direction at a temperature of Tg.about.Tg+30.degree.
C. The transverse direction drawing is conducted at a temperature
of Tg+10.degree. C..about.Tg+40.degree. C.
[0033] If the longitudinal drawing is conducted at a temperature
lower than Tg, or if the transverse drawing is conducted at a
temperature lower than Tg+10.degree. C., the surface of film
becomes cloudy due to the cold drawing. On the other hand, if the
longitudinal drawing is conducted at a temperature higher than
Tg+30.degree. C., or if the transverse drawing is conducted at a
temperature higher than Tg+40.degree. C., the twist wrapping
property becomes poor due to excessive degree of
crystallization.
[0034] Further, it is preferable that the drawing ratio in the
transverse direction is not less than 2, and the product of the
drawing ratios in the longitudinal and transverse directions is in
the range of 4 to 20. The crystallization degree of a biaxially
oriented polyester film prepared as described above become less
than 40% (corresponds to a specific gravity of 1.38 in case of
polyethylene terephthalate), and such a film shows improved twist
wrapping property. If the transverse drawing ratio is less than 2,
the film thickness becomes non-uniform. Therefore, it is preferable
that the drawing ratio in the transverse direction is kept at 2 or
higher.
[0035] Further, if the product of the drawing ratios in the
longitudinal and transverse directions is less than 4, the film
orientation in the longitudinal direction is not sufficient and,
therefore, the film tears easily in the transverse direction during
the film making process. On the other hand, if the product of the
drawing ratios is more than 20, the film orientation becomes
excessive and the twist wrapping property of the film
deteriorates.
[0036] It is preferable that the biaxially oriented polyester film
has a refractive index of more than 1.6, either the longitudinal or
transverse direction.
[0037] The dead-fold retainability in the longitudinal and
transverse directions of the inventive film is at least 60%,
preferably at least 70%. If the dead-fold retainability is less
than 60%, the twist wrapping property becomes unsatisfactory.
[0038] Further, the twisting property in the transverse direction
of the film is dependent on the dead-fold retainability in the
longitudinal direction of the film. On the other hand, the twisting
property in the longitudinal direction of the film is dependent on
the dead-fold retainability in the transverse direction of the
film. Therefore, depending on the use of film, the dead-fold
retainability in either direction of is preferably kept at 60% or
higher. Preferably, the inventive film has a dead-fold
retainability of at least 60% in both directions.
[0039] The present invention is further described and illustrated
in Examples, which are, however, not intended to limit the scope of
the present invention.
[0040] The polyester films manufactured in examples were examined
for the following properties.
[0041] (1) Specific Gravity: Density gradient tube method (ASTM
D1505, JIS K7112)
[0042] (2) Refractive Index: Refractive indexes in the longitudinal
and transverse directions of film were measured with Abbe
Refractor
[0043] (3) Dead-fold retainability (%)
[0044] a. Transverse Direction
[0045] As shown in FIG. 1, a film specimen (10) of 10 cm
(transverse direction).times.1 cm (longitudinal direction) is
folded at the 9 cm point in the transverse direction. Using a
pressure applying means (20) (Sentinel Brand Machine, Model No.
12-AS, Hot-Press, Packaging Industries Group, Inc., Hyannis, Mass.
02601, USA), a pressure of 30 psi is uniformly applied on the
folded part of the film specimen at room temperature
(23.about.25.degree. C.) for 3 seconds as shown in FIG. 2. Then,
the film specimen is kept at a vertical position for 1 hr and the
angle (.theta.) formed at the folded part of film specimen was
measured. Dead-fold retainability (%) are determined as following
equation.
Dead-fold retainability(%)=(180-.theta.).times.100 180
[0046] b. Mechanical Direction
[0047] The above procedure was repeated using a film specimen (10)
of 10 cm (transverse direction).times.1 cm (longitudinal
direction).
[0048] (4) Twist fixation in transverse direction
[0049] As shown in FIG. 4, a film specimen of 10 cm (transverse
direction).times.7 cm (longitudinal direction) is prepared and hard
candy was wrapped therewith by 540.degree. twisting (1.5 turn) in
the transverse direction. The wrapped candy was left standing for
24 hrs and the maintained twisting angle was measured. Twist
fixation is determined as follows:
Twist fixation(%)=maintained twist angle/initial twist angle
(540.degree.)
[0050] (5) Glass transition temperature:
[0051] Differential Scanning Calorimeter (Perkin-Elmer DSC-7)
[0052] Temperature rising 20.degree. C./min
[0053] (6) Film Strength (ASTM D882):
[0054] Strength at break was measured using 100 mm.times.15 mm
specimen at a rate of 200 mm/min and at room temperature
(23.+-.2.degree. C.).
[0055] (7) Film thickness difference:
[0056] The film thickness was measured at 50 points which were
arranged at 5 cm intervals in both the longitudinal and transverse
directions.
Thickness difference(%)=(Tmax-Tmin).times.100/Tave
[0057] wherein Tmax is maximum thickness of film; Tmin is minimum
thickness of film; and Tave is average thickness of film.
EXAMPLE 1
[0058] 100 parts by mole of dimethyl terephthalate and 180 parts by
mole of ethylene glycol were placed in an autoclave equipped with a
distillation column, heated to 150.degree. C., and manganese
acetate (an interesterification catalyst), was added thereto in an
amount of 0.05% by weight based on the weight of dimethyl
terephthalate. While removing methanol formed, the temperature was
raised to 220.degree. C. over a period of 120 min. After the
interesterification was complete, trimethylphosphate (a stabilizer)
was added in an amount of 0.045% by weight based on the weight of
dimethyl terephtalalte, and silicon dioxide having an average
particle diameter of 2 micron (an antiblocking agent) was added in
an amount of 0.1% by weight based on the amount of dimethyl
terephthalate. After 10 minutes, antimonytrioxide (polymerization
catalyst) was added in an amount of 0.03% by weight based on the
weight of dimethyl terephthalte, and the resulting product was
transferred to a second reactor equipped with a vacuum unit, and
reacted at 280.degree. C. for about 140 minutes, to obtain a
polyethylene terephthalate (Tg 78.degree. C.) having an intrinsic
viscosity of 0.66 dl/g.
[0059] The polyester thus obtained was melted at 280.degree. C.,
extruded through a T-die having a width of 820 mm, and cooled by a
casting roller maintained at 30.degree. C., to obtain an amorphous
sheet of 780 mm width and 225 micron thickness. The amorphous sheet
was drawn at a ratio of 3 in the longitudinal direction at
94.degree. C., and then, drawn 3 times in the transverse direction
at 100.degree. C., to obtain a biaxially drawn polyester film of
2,250 mm wide and 25 micron thick.
[0060] The drawing conditions for polyester film obtained above are
shown in Table 1, and properties of the film, i.e., film strength,
specific gravity, crystallization, refractive index, dead-fold
retainability and twist fixation measured, in Table 2.
EXAMPLES 2 TO 10 AND COMPARATIVE EXAMPLES 1 TO 5
[0061] The procedure of Example 1 was repeated except that various
drawing conditions shown in Table 1 were used. The properties and
resulting of biaxially oriented polyester films are shown in Table
2.
1 TABLE 1 Longitudinal Transverse Sheet Direction(LD) Direction(TD)
Total Biaxially oriented film Example Thickness Temp. Temp. Drawing
Width Thickness Difference No. (micron) (.degree. C.) Ratio
(.degree. C.) Ratio ratio (mm) (micron) (%) 1 225 94 3.0 100 3.0 9
2250 25 3 2 263 98 3.5 100 3.0 10.5 2250 25 3 3 188 91 2.5 100 3.0
7.5 2250 25 4 4 158 88 2.1 100 3.0 6.3 2250 25 5 5 263 94 3.0 104
3.5 10.5 2625 25 3 6 188 94 3.0 98 2.5 7.5 1875 25 6 7 150 94 3.0
98 2.0 6 1500 25 7 8 306 97 3.5 104 3.5 12.25 2625 25 3 9 219 91
2.5 104 3.5 8.75 2625 25 3 10 219 97 3.5 98 2.5 8.75 1875 25 4 Com.
563 94 5.0 100 4.5 22.5 3150 25 2 Ex. 1 Com. 225 125 3.0 100 3.0 9
2250 25 3 Ex. 2 Com. 225 94 3.0 130 3.0 9 2250 25 3 Ex. 3 Com. 225
125 3.0 130 3.0 9 2250 25 4 Ex. 4 Com. 68 94 1.5 100 1.8 2.7 1350
25 20 Ex. 5
[0062]
2TABLE 2 Dead-fold Film strength retainability Refractive Twist
Example (kgf/mm2) Specific Crystallization (%) index Fixation No.
LD TD gravity (%) LD TD LD TD (%) 1 22 22 1.355 18 84 86 1.633
1.635 85 2 24 22 1.357 20 82 80 1.637 1.634 82 3 20 22 1.352 15 86
88 1.628 1.636 87 4 18 22 1.350 13 90 90 1.621 1.636 90 5 23 26
1.360 22 80 82 1.632 1.638 81 6 22 20 1.353 16 86 84 1.634 1.629 85
7 21 18 1.351 14 88 88 1.635 1.627 90 8 25 24 1.362 24 78 78 1.637
1.638 80 9 20 25 1.354 17 84 86 1.631 1.639 84 10 25 20 1.354 17 84
84 1.638 1.63 84 Comp. Ex. 1 27 28 1.388 46 42 42 1.655 1.658 40
Comp. Ex. 2 23 22 1.385 44 50 50 1.634 1.635 45 Comp. Ex. 3 22 24
1.386 45 45 45 1.634 1.634 48 Comp. Ex. 4 23 23 1.392 50 40 40
1.634 1.633 35 Comp. Ex. 5 a a a a a a 1.588 1.592 broken a) a
satisfactory film was not formed due to poor processibility.
[0063] Using each of the biaxially oriented polyester films
obtained Examples 1 to 10 and Comparative Examples 1 to 5, hard
candies were twist wrapped at a rate of 600 pieces/min. If the film
was broken during the wrapping process, or if more than 5% of the
packed candies were released after 24 hrs is more than 5%, the film
was evaluated as "poor". As shown in Table 2, the film of Examples
1 through 10 show improved properties for twist wrapping, while the
films of comparative examples 1 through 5 were evaluated as
poor.
[0064] Thus, the inventive biaxially oriented polyester films has
good dead-fold retainability which is useful for twist wrapping of
candies in addition to intrinsic properties of polyester film such
as high thermal stability, weatherability, physical properties and
chemical resistance.
[0065] While the invention has been described with respect to the
above specific embodiments, it should be recognized that various
modifications and changes may be made to the invention by those
skilled in the art which also fall within the scope of the
invention as defined by the appended claims.
* * * * *